The present invention relates generally to dehydrogenation catalysts and to catalytic dehydrogenation reactions employing the same. In preferred forms, the present invention relates to catalysts employed in dehydrogenation of cyclohexanol to produce cyclohexanone.
It is well known that cyclohexanol can be catalytically dehydrogenated to produce cyclohexanone, as evidenced, for example, by U.S. Pat. No. 2,640,084.1 In this regard, various catalysts have been proposed for such catalytic dehydrogenation processes. For example, in the above-cited U.S. ""084 patent, a nickel dehydrogenation catalyst is proposed having copper (mostly in the form of copper metal) and chromium (mostly in the form of its oxide) which has been stabilized by the presence of an alkali metal sulfate. U.S. Pat. No. 4,310,703 discloses that a copper-chromium catalyst derived from a mixture of copper oxide and chromium oxide can be employed in the catalytic dehydrogenation of cyclohexanol to form cyclohexanone. Furthermore, U.S. Pat. No. 4,417,076 notes that a mixture of nickel with a promoter (e.g., germanium and/or lead) is usefully employed in the dehydrogenation of cyclohexanes into their corresponding cyclic ketones. Catalytic mixtures of copper oxide and zinc oxide for dehydrogenation of cyclohexanol to form cyclohexanone are suggested by U.S. Pat. Nos. 4,918,239 and 4,670,605.
1The entire contents of this, and all other, publications hereinafter cited are expressly incorporated hereinto by reference. 
While various catalysts for dehydrogenation processes to convert cyclohexanol to cyclohexanone are known generally, there still exists a need to provide catalysts with superior conversion and selectivity properties. It is towards fulfilling such a need that the present invention is directed.
Broadly, the present invention is embodied in dehydrogenation catalysts and catalytic dehydrogenation processes using the same. The catalysts of the present invention more specifically is embodied in catalyst mixtures comprised of zinc oxide (ZnO), calcium carbonate (CaCO3) or calcium oxide (CaO), and an amount of chromium (III) oxide (Cr2O3) in an amount sufficient to improve conversion and/or selectivity of cyclohexanol to cyclohexanone under cyclohexanol dehydrogenation conditions.
These and other aspects and advantages will become more apparent after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.
The catalysts of the present invention will necessarily include zinc oxide, calcium carbonate or calcium oxide and chromium (III) oxide. The zinc oxide is most preferably present in the catalysts of the present invention in amounts ranging between about 45 wt. % to about 60 wt. %, and more preferably in an amount of about 55 wt. % (+/xe2x88x92 about 5 wt. %).
The calcium carbonate or calcium oxide may be included in the catalysts of the present invention in amounts ranging between about 25 wt. % to about 45 wt. %, and more preferably between about 30 wt. % to about 35 wt. % (+/xe2x88x92 about 5 wt. %). The catalysts of the present invention may be formulated initially to include calcium carbonate, with the catalyst being controllably heated to convert the calcium carbonate to calcium oxide prior to being placed in service.
Chromium (III) oxide (Cr2O3) is present in the catalysts of the present invention in amounts sufficient to improve conversion and/or selectivity of cyclohexanol to cyclohexanone under cyclohexanol dehydrogenation conditions. The chromium (III) oxide is present in amounts ranging from about 0.2 wt. % to about 30 wt. %, more preferably 1.5 wt. % to about 20 wt. %, and most preferably between about 2.5 wt. % and 15 wt. %.
The catalysts of the present invention may include other optional constituents that are typically employed in dehydrogenation purposes. For example, the catalysts of the present invention most preferably include sodium oxide (NaO) in an amount between about 0.1 to about 3.0 wt. %, and more typically in an amount of about 0.5 wt. % to about 1.5 wt. %.
The catalysts of the present invention will typically exhibit bulk densities of between about 700 g/l to about 1250 g/l, porosities of between about 0.10 to about 0.35 cm3/g, and a hardness (kgf) of between about 8.0 to about 15.0.
In use, the catalysts of the present invention will be placed in a suitable dehydrogenation reaction vessel which is supplied with a cyclohexanol-containing feed stream under conventional dehydrogenation conditions. The cyclohexanol in the feed stream will thereby be dehydrogenated to form cyclohexanone according to known reaction mechanisms.